Electrophotographic developers are a dry developer in which toner components composed of materials containing a colorant and a resin binder are used in a dry state, and a liquid developer in which toner components are dispersed in an insulating liquid.
In a liquid developer, toner particles are dispersed in oil in an insulating liquid, thereby making it possible to form smaller particle sizes as compared to a dry developer. Therefore, high-quality printouts can be obtained surpassing offset printing, so that the liquid developer is suitable for commercial printing applications. In the recent years, with increasing demands for speeding up, liquid developers having lowered viscosities have been desired. In other words, a liquid developer in which toner particles are stably dispersed in a smaller particle size and a lowered viscosity has been desired.
Patent Publication 1 discloses a liquid developer containing a polymeric dispersant obtained by polymerizing an ethylenically unsaturated monomer having an amino group with an ethylenically unsaturated monomer containing an alkyl group having from 4 to 24 carbon atoms, and a plasticizer which is insoluble in a carrier liquid having a melting point of 25° C. or higher, which is intended for providing a liquid developer capable of obtaining stable output images over a long period of time by having excellent fusing ability, offset resistance, and color developability, and also having excellent storage stability.
Patent Publication 2 discloses a liquid developer characterized in that the liquid developer contains toner particles and a basic polymeric dispersant, wherein the toner particles are made of resins containing a vinyl-based copolymer resin composed of styrene which may have one or two alkyl groups having from 1 to 4 carbon atoms and/or an alkyl (meth)acrylate and/or acrylic acid and methacrylic acid, and a polyester resin containing, as an acid component, an aromatic compound having three or more functional groups in a proportion of 5% by mol or more and 50% by mol or less of the entire acid component, wherein the vinyl-based copolymer resin and the polyester resin are contained in a ratio of from 1:9 to 9:1, which is intended for providing a liquid developer which is excellent in both cardboard fusing ability and document offset property.
Patent Publication 1: Japanese Patent Laid-Open No. 2014-92579
Patent Publication 2: Japanese Patent Laid-Open No. 2012-58389